It is known for the tubular case which is required for the production of sausages or similar portion packs to be continuously or intermittently produced by means of such an apparatus on site by longitudinal seam sealing of a film strip which is transformed into a tubular configuration. In that respect the term sealing is used to denote any kind of (non-releasable) connection of the two longitudinal edges, including for example welding as the preferred sealing process but also adhesive or the like. In the process of the general kind to which this invention relates, as is known from EP 0 908 103 A1, the film strip is drawn by the advance drive means arranged in the region of or downstream of the sealing device in the transport or filling expulsion direction, by way of a suitable transformation device (shaping shoulder) and through the sealing or welding means. The shaping shoulder surrounds the filling tube and transforms the film strip around the filling tube into a configuration such that the longitudinal edges thereof adjoin each other either in butting or overlapping relationship. Those longitudinal edges are connected together directly or by means of a sealing strip connecting the edges, in the subsequent welding or sealing device.
The film tube formed in that way is further conveyed by the advance drive means in the filling expulsion direction into a buffer portion on the filling tube, in which it is folded harmonica-like to constitute a reserve supply. A reserve supply is necessary as the filling operation takes place intermittently and the sealing operation takes place continuously in most cases and also intermittently in some cases, but at any event slower than the withdrawal of the film tube from the filling tube, which is governed by the filling expulsion during the filling operation. On the other hand, there are pauses after the filling operation, while the ends of the filled film tube are being closed by means of a so-called clip machine. Therefore the film tube continues to be produced even during the clipping pauses (stoppage of the filling arrangement) in which the filling operation is stopped. In that situation the film tube reserve supply builds up in front of a retaining means.
In order to achieve synchronisation between film tube production and the filling operation, it is known that film tube production is regulated. For that purpose the above-mentioned measuring device for determining a supply amount of the film tube is used, which typically comprises a sensor element movable with respect to the filling tube and a stationary sensor element. The movable sensor element is connected to an entrainment member which engages into the cross-section of the folded or gathered-together film tube and which at the same time forms the retaining means for the film tube supply. When the supply is increased in size, it displaces the entrainment member and the movable sensor element in the conveyor direction of the advance drive means against a return force which is applied for example by a spring (spring force) or a pneumatic element (pressure force). When film tube is taken from the supply and the supply thus decreases in size, then the return force drives the entrainment member with the movable sensor element back in the opposite direction to the conveyor direction.
In the simplest configuration of the measuring device the fixed sensor element has for example two spaced mechanical or magnetic switches or signalling devices which are respectively actuated when the movable sensor element approaches (mechanical or contact-less contact surface). In that situation the switches trigger the apparatus to be switched off or on, at a preselected maximum and minimum supply amount respectively, which is selected by a suitable relative arrangement of the switches/signalling devices and contact surfaces.
A further development of a measuring device provides for travel measurement between the movable and the stationary sensor elements, the result thereof permitting differentiated adaptation of the sealing and conveyor speed to the supply amount.
At any event however the movable sensor element is transported by the entrainment member which engages into the cross-section of the gathered-together film tube. That presupposes in each case that the reserve supply adopts a sufficiently folded configuration which is engaged by the entrainment member. Now however there are films with coatings which suffer damage due to being heavily folded. For example films with an aluminium coating are sensitive to sharp bends as the relatively brittle aluminium layer can tear at such locations, whereby both the functional and also the aesthetic properties of the film are adversely affected. The same applies for stiff film materials which, after sharp transformation thereof, can no longer be completely smoothed out and thus retain an irreversible, undesirably corrugated and wavy structure. In addition the problem arises that the folds in the film which is still hot after the sealing operation stick to each other in the event of an excessively high pressure being applied to the accumulated film material while it is forming the reserve supply.